1. Technical Field
One or more embodiments of the present invention relates to electrostatic actuators in general, and in particular for example, to methods and apparatus for controlling undesirable arcuate motion in them.
2. Related Art
Actuators for use in miniature cameras and other devices are well known. Such devices typically comprise voice coils that are used to move a lens for focusing, zooming, or optical image stabilization.
Microelectromechanical systems (MEMS) actuators are also known. Examples of MEMS actuators include electrostatic comb drives, scratch drives, and thermal drives. Microminiature electrostatic MEMS actuators can be fabricated using well known wafer-scale integrated circuit (IC) fabrication techniques, and can be used in a variety of applications. For example, electrostatic MEMS actuators can be used to move an objective lens so as to effect autofocus, zoom and image stabilization functions in miniature cameras useful in various host devices, e.g., mobile phones, computers, laptops, personal digital assistants (PDAs), surveillance cameras and the like. Accordingly, it is desirable to provide improved electrostatic MEMS actuator devices for such applications.
Electrostatic MEMS actuators are susceptible to a problem known as “arcuate motion.” In particular, the comb drives of such actuators include a plurality of interdigitated fingers or teeth, portions of which are attached to a fixed stage or frame, and portions of which are attached to a moving frame. It is desirable that the teeth of the comb drives move substantially parallel to each other during operation to avoid contact, interference, “stalling,” and “chattering” problems, which in turn, requires the moving frame to move substantially parallel to the fixed frame. However, due to the nature of the resilient parallel motion flexures that couple the moving frame to the fixed frame, the former necessarily experiences some second order arcuate movement relative to the latter during movement, which if not controlled, can lead to the foregoing and other problems.
Accordingly, a long-felt but as yet unsatisfied need exists for inexpensive yet reliable methods and apparatus for controlling, compensating, and/or accommodating arcuate motion in the comb drives of electrostatic actuators.